1. Field of the Invention
The present invention is directed to an underdrain system, and, in particular, an underdrain system and method for transferring forces and directing flow.
2. Description of Related Art
The main components of an underdrain system are filtering media and underdrain blocks. Underdrain blocks are generally square or rectangular in cross section and have a long longitudinal axis as compared to their cross section. They are attached end-to-end to form long sections called laterals. When using a mono-pour installation method, underdrain laterals are attached to a filter floor using a series of anchor rods, horizontal supports, and grouting. Filtering media sits atop these underdrain blocks. The underdrain system may also utilize a flume, a deeper channel set into the floor of the filter through which backwash fluid and, optionally, air may be introduced into the system.
Current molded plastic underdrains on the market do not have multiple protrusions or internal features along the inside of the underdrain block due to manufacturing requirements. The lack of internal features in the underdrain block greatly limits the strength of the overall assembly. Particularly, downward loads that are applied to the top of the underdrain during normal operation of the system cannot be transferred to the outside walls of the underdrain block and into the concrete fill material adjacent to the underdrain. The downward force must be taken up by the top deck of the underdrain block and any connecting walls of a primary chamber formed within the underdrain block. Further, internal pressure or forces exerted in the primary chamber of the underdrain block during the backwash sequence act on the walls of the primary chamber and any portion of the top deck surface of the underdrain block that is in direct connection to the primary chamber. However, no forces are transferred from the primary chamber to the vertical outside walls of the underdrain block during a backwash sequence.
In addition, the lack of internal features also limits the overall hydraulic performance of the system. For instance, a dual parallel underdrain includes a primary chamber and secondary chambers formed within the underdrain block. Fluid passes from the primary chamber into the secondary chamber through a series of orifices formed along the length of the primary chamber. Flow in the secondary chamber will balance or compensate prior to discharge through secondary chamber orifices. The balance and compensation of flow in the secondary chamber is critical to the overall performance of the system. Because current underdrain blocks lack internal features, it is difficult to dissipate the energy of fluid passing through the primary chamber water orifices, which limits the overall hydraulic performance of the system.
In view of the foregoing, a need exists for an underdrain system that is more effective at transferring forces and directing fluid flow.